Protective rain shield and electric field grading apparatus for use on a high voltage insulator



C. F. E RAIN US FOR Aug. 5, 1969 SONNENBERG ET AL 3,459,881

SHIELD AND ELECTRIC FIELD GRADING USE ON A HIGH VOLTAGE TNSULATOR 1 y 2 Sheets-Sheet 1 PROTECTIV v APPARAT Filed Nov. 16, 1967 INVENTORS Charles F. Sonnenberg Joseph J. whneslde and Dennis G. Pointer WW W ATTORNEY 3,459,881 D ADING s TOR 2 Sheets-Sheet 2 C. F. SONNENBERG ET AL IVE RAIN SHIELD AND ELECTRIC F ATUS FOR USE ON A man VOLTAGE Aug. 5, 1969 PROTECT PAR Filed Nov. 16. 7

3,459,881 Patented Aug. 5, 1969 US. Cl. 174-144 8 Claims ABSTRACT OF THE DISCLOSURE The electrically conductive device has a portion thereof forming a substantially smooth frusto-conical surface sloping downward away from the insulator on which it is mounted, and an annular portion forming at least a substantially arcuate cross-section of a toroidal ring, the toroidal ring shaping the electric field in the area adjacent the outside circular edge of the frusto-conical portion whereby corona producing stresses are avoided; in some embodiments the circular edge extends radially from the insulator beyond the outside diameter of the ring portion whereby rain running off of the frusto-conical portion runs freely downwardly beyond the ring portion. Other embodiments employ specially shaped run-off lips which may be secured to, or form part of, the toroidal ring.

Background of the invention The invention relates to rain shields for use on column insulators which are exposed to the weather, the rain shields assisting in keeping the insulation dry whereby the flashover characteristic of the insulator is maintained at substantially that which would be experienced under dry conditions rather than wet conditions. In addition, the rain shield may prevent some contaminant from forming on the insulator and the sheds thereof.

Description of the prior art Rain shields and field grading rings have been employed heretofore but they are relatively complicated and expensive to manufacture, and difficulty has been encountered in providing the necessary rain Wash-off without producing a sharp electric field gradient which resulted in the formation of corona.

Summary of the invention A conductive toroidal ring is attached by or to a conductive slanting disc-like cover or plate, to the metallic terminal at the exposed end of the insulator, as by peripherally spaced bolts. The cover may be thought of as frusto-conical or having an inverted bowl shape. Secured to the cover at or near the outer edge thereof as by soldering or brazing is a ring composed of conductive material. The cover and grading ring apparatus includes means forming a rain wash-off lip or surface, which may be means secured to the ring to form the rain wash-off device, which may be an obliquely slanting lip, which may be substantially an extension of the cover, a downwardly extending annular lip, a specially formed annular lip, a wire soldered around the outside of the ring in an annular path, a slanting lip with a wire soldered around the outside or lower edge thereof, a ring having an arcuate gap therein with one edge of the ring at the gap extending beyond the other annular edge and providing for wash-off,

of the insulator not being shown for simplicity of illustra- 4 tor may be shaped generally in the form of a ring to provide rain wash-off while avoiding any configuration which would result in the production of corona.

Brief description of the drawings FIGURE 1 is a fragmentary view in section of rain shield grading ring apparatus according to one embodiment of our invention, showing the generally frustoconical cover secured to a column insulator, a term used in the trade frequently with respect to a hollow, tubular insulator structure, the toroidal ring secured to or near the outward edge of the cover, and the annular lip for wash-off of water from the toroidal ring, it being seen that the insulator is generally tubular in shape, the other half of the insulator not being shown for simplicity of illustration, and that the toroidal ring extends around the entire insulator and around or near the entire outer edge of the cover.

FIG. 2 shows a modification of the rain shield of FIG. 1 in which the run-off lip extends in a generally downward direction.

FIG. 3 shows a modification of the invention of FIG. 1 in which a run-off lip or cover edge forming the run-off lip extends at still a different angle with respect to the toroidal ring and the longitudinal axis of the insulator and is in effect an extension of the frusto-conical surface.

FIGS. 4 and 5 show rain shields according to another embodiment of the invention in which the run-ofi lip has a further configuration.

FIGS. 6 and 7 show a modification of the invention in which an annular extending wire is soldered or otherwise fastened either to the side of the toroidal ring or at or near the outer edge of an annular lip extending therefrom;

FIG. 8 shows a further embodiment of our invention in which the generally frusto-conical cover plate has the outer edge thereof curved generally to resemble in crosssection a toroidal ring, with a relatively sharp edge at the bottom thereof at the outside to provide wash-off, and an inwardly extending edge extending toward the axial center of the ring to prevent corona; and

FIG. 9 shows our invention according to still a further embodiment thereof in which the toroidal ring has an arcuate gap extending therearound with one edge at the gap extending beyond the other edge at the gap and providing a wash-off for rain.

Description of the preferred embodiments Particular reference is made now to FIG. 1 where an insulator generally designated 11 is shown generally in the form of a sleeve or tube of, for example, porcelain, having sheds 12 at spaced intervals along the length thereof, and having an outer terminal structure 13 composed of conductive material and Which is electrically connected to a high voltage line. Secured to the outer terminal structure 13 as by peripherally spaced bolts, one of the bolts being shown at 14, is a generally frusto-conical or inverted bowl cover plate 15 composed of conductive material. Secured underneath the outer edge of the cover plate 15 as by an annular weld 16 is a toroidal ring 17 having secured thereto, as by solder 18, a slightly downwardly extending annular lip 19 which extends around the entire toroidal ring.

In constructing the rain shield, the annular weld 16 may be replaced by a soldered joint on the upper surface of toroidal ring 17, in which case the solder is machined or polished to make a smooth surface. Solder connection 18 is also smoothed, polished or machined to make .a smooth surface and prevent the formation of a circular path or circular area of high electrical gradient. The length of the lip 19 is carefully chosen in accordance with the dimensions of the rain shield cover and ring, the dimensions of the insulator, and the voltage which will be applied to the insulator terminal structure so that no substantial corona formation results from the wash-off lip 19.

In operation it is seen that the downwardly extending cover plate extends well beyond the sheds of the insulator, protecting the sheds from rain and enhancing the flashover characteristics of the insulator in wet weather as well as preventing contaminant from collecting on the sheds and in the spaces on the body of the insulator between sheds. The toroidal ring provides for a substantially uniform electric or electrostatic field existing between the ring and the bottom end of the insulator in which central post 50 of conductive material is assumed to be a surface of opposite polarity with respect to terminal structure 13, or which it is assumed is at ground potential. The toroidal ring prevents the formation of large electric field gradients. The aforementioned lip 19 provides a run-off for rain so that it does not run around the lower portion of the toroidal ring 17 and perhaps contaminate the lower surface of the ring.

Particular reference is made now to FIG. 2 where for simplicity of illustration the insulator structure is not shown, and where the toroidal ring 17 is shown to have the lip .19 extending in a substantial downward direction, to provide wash-off.

Particular reference is made now to FIG. 3 where the annular lip 19" may be, and is seen as substantially an extension of the frusto-conical surface of cover plate 15.

Particular reference is made now to FIGS. 4 and 5 where again for simplicity of illustration the insulator structure is not shown, but it will be understood that the frusto-conical cover 'plate 15 composed of conductive material is secured to the outer terminal structure of the insulator. In the embodiments of FIGS. 4 and 5, a specially shaped lip 22 and 22' respectively is secured to the toroidal ring 17, the lip in both figures being shaped to provide wash-off and being soldered, welded or brazed in an annular path around the toroidal ring. The underneath surface of the run-off lip 22', FIG. .5, which lip is substantially triangular in cross-section, is seen to be slightly concave, thereby preventing water which may adhere to the run-off lip from flowing back on to the toroidal ring 17.

Particular reference is made now to FIG. 6 where a wire 25 is seen to extend around the entire toroidal ring forming a wash-off and to be secured thereto by a polished annular solder connection 26.

Particular reference is made now to FIG. 7 where a toroidal ring 17 is seen to have .an annular extending lip 28 around the entire periphery thereof with a wire 29 soldered or otherwise secured to the edge of the lip remote from the ring. The length of the lip 28 as well as the size of the wire and their position on the toroidal ring are carefully chosen to provide desired wash-off without resulting in the formation of corona.

Particular reference is made now to FIG. 8. A generally frusto-conical cover plate 31 is seen to have the outer edge thereof bent to generally form a ring portion 32 with a relatively sharp lower outer annular edge 33 to provide wash-off and a curved inwardly extending edge 34 curved inwardly toward the circular axis of the ring to prevent the formation of corona.

Particular reference is made now to FIG. 9; cover plate 40 secured to the end of the insulator being generally of an inverted bowl shape or frusto-conical shape and slanting downwardly and away from the insulator, has a toroidal ring 41 secured thereto with an arcuate gap therein extending around hte entire ring, the edge 42 of the ring being shown as extending slightly beyond the other anneclar edge 43 forming the gap 44, so that rain runs off of the edge 42 of the ring at the gap and does not flow around to the undersurface.

Summarizing, the recent emphasis on the wet switching surge characteristics of apparatus, particularly in the extra high voltage range, has made it more important to consider the water shedding characteristics and the resulting effect on the electrical fiashover strength.

Of prime importance is the need to prevent elevated live metal parts from dropping cascading streams of water onto the support porcelain. These streams are often more concentrated than ordinary rainfall and thus cause external electrical fiashovers at undesirably low voltages in prior art apparatus. Our invention includes the combination of an inverted saucer type shield with an electrostatic grading ring secured to the shield at or near the extremity thereof. This provides excellent electrostatic shielding of the rain shield, thus preventing the formation of corona on what would have been its sharp outer lip. The corona is undesirable as it caused premature flashover and/or excessive radio influence voltage (RIV). We provide a relatively sharp outer lip so that water is forced to drop off the shield rather than rolling around to the underside. The shield overhangs the porcelain support column to insure the dropping of water beyond the porcelain. One disadvantage of prior art rain shields is that the streams roll around the edge and this protection margin is lost.

Our rain shield grading ring structure is especially suitable for use with a current transformer, the shielding .and protection of which is generally more difficult because there is no overhanging tank to electrostatically shield an underhanging rain shield; the porcelain columns diameter is much larger, requiring a very large diameter rain shield in order to efliectively protect the column from water cascades; the central grounded post within the porcelain column, shown at 50 in FIG. 1, complicates the external electrostatic field, making it undesirable to consider either a large diameter rain shield or an edge so sharp as to produce corona; and the absence of the overhanging tank and bushing coupled with the large diameter, means that the current transformer rain shield will have a severe proximity effect on the circuit breaker columns flashover characteristic unless the rain shields position and edge conditions are carefully considered.

All embodiments of our invention provide the proper electrostatic grading for the supporting insulating column and any live parts, protect the column from excessive cascading water streams, prevent water from rolling around the outer edge of the grading ring, andmaintain a satisfactory RIV and corona level.

Further summarizing, we mount a toroidal ring about the upper section of the insulating column to provide electrostatic shielding. A cover of conductive material between the column top and intersecting or approaching the ring tangentially sheds all water which is running toward the insulating column out and over the toroidal ring. We insure that the toroidal ring cover assembly is provided with or includes a drip lip or contour shape to force water streamlets to drip or run off the outermost edge; the RIV and/or corona level of the assembly is kept at a satisfactory level by keeping the drip lip protuberance within the electrostatic shadow of the large diameter grading ring and by the use of the large diameter ring at the edge of the rain shield instead of the usual sharp edge. Thus, our grading ring serves a triple purpose, shielding the column, the elevated live metal parts, and the edge of the rain shield.

In practice, the use of the rain shield grading ring combination of our invention results in an improvement in wet switching surge strength.

We claim as our invention:

1. As an article of manufacture, a protective device composed of electrically conductive material adapted to be mounted on the upper end of a high voltage insulator mounted in a substantially vertical position and exposed to rain and other weather conditions, said device being adapted to be electrically connected to the line supported by the insulator, said insulator being adapted to have conductive means at the other end thereof at a polarity other than that of the line, a portion of said device forming a substantially smooth frusto-conical surface sloping downward away from the insulator, an annular portion of said device forming at least a substantial arcuate cross-section of a toroidal ring the major portion of which is beneath the portion forming the frusto-conical surface, the toroidal ring shaping the electric field between the line and conductive means in the area adjacent the outside circular edge of the frusto-conical portion whereby corona producing stresses are avoided, said circular edge extending radially from the insulator beyond the outside diameter of the toroidal ring whereby rain running off the frusto-conical portion runs freely downwardly beyond the ring.

2. Protective apparatus for a high voltage line supporting insulator adapted to be mounted in a substantially vertical position and exposed to rain and other weather conditions, including conductive means forming a substantially smooth frusto-conical surface adapted to be mounted on the end of the insulator and sloping downwardly away from the insulator and adapted to be at the potential of the high voltage line supported by the insulator, the outer annular edge of said means having a diameter substantially larger than the outside diameter of the insulator whereby the outer surface of the insulator is protected from rainfall, the other end of the insulator being adapted to have conductive means secured thereto at opposite polarity to the line, and toroidal ring means composed of conductive material secured to the conductive frusto-conical means around the underside thereof in electrical contact therewith, the toroidal ring means preventing the formation of an electric field at the edge of the frusto-conical means which produces corona, the outer annular edge of said frusto-conical means extending sufficiently far beyond the ring means that water from the last named edge runs 01f at positions beyond the outer extremity of the ring means.

3. For use with a high voltage insulator, the combination of a generally frusto-conical shaped cover plate composed of electrically conductive material adapted to be secured to the outer terminal structure of the insulator, and at least one toroidal electric field grading ring composed of conductive material secured to the cover plate near the outer annular edge thereof, said ring having an arcuate gap extending therearound in the wall thereof farthest from the insulator with the upper annular edge of the ring adjacent the gap extending with respect to the axis of the insulator radially byeond the lower annular edge of the ring at the gap, water streamlets running off of said upper annular edge of the ring without substantial splashing on the insulator.

4. For use with a high voltage insulator, the combination of a generally frusto-conical shaped cover plate composed of electrically conductive material adapted to be secured to the outer terminal structure of the insulator, and at least one toroidal electric field grading ring means composed of conductive material secured to the cover plate near the outer annular edge thereof, the toroidal ring means and cover plate including means constructed and arranged to provide that water streamlets run off without running around to the underside of the toroidal ring means and without substantial splashing on the insulator, said means providing that water streamlets run off including an annular drip lip extending around the entire periphery of the ring means, the' drip lip being composed of an annular strip of metal of narrow crosssection secured to the annular toroidal ring means, said strip of metal slanting from the toroidal ring means and forming a water run-01f, the upper surface of said strip forming substantially a continuation of the frusto-conical surface of the cover plate.

5. For use with a high voltage insulator, the combination of a generally frusto-conical shaped cover plate composed of electrically conductive material adapted to be secured to the outer terminal structure of the insulator, and at least one toroidal electric field grading ring means composed of conductive material secured to the cover plate near the outer annular edge thereof, the toroidal ring means having means forming an annular drip lip extending around the entire periphery thereof at a predetermined position thereon, said annular drip lip being substantially triangular in shape with a slightly concave bottom surface.

6. For use with a high voltage insulator, the combination of a generally frusto-conical shaped cover plate composed of electrically conductive material adapted to be secured to the outer terminal structure of the insulator, and at least one toroidal electric field grading ring means composed of conductive material secured to the cover plate near the outer annular edge thereof, the toroidal ring means having means forming an annular drip lip extending around the entire periphery thereof at a predetermined position thereon, said annular drip lip including a wire extending around the outside of the toroidal ring means and secured thereto by means forming a smooth surface extending from the outer surface of the toroidal ring means to the outer surface of the wire.

7. For use with a high voltage insulator, the combination of a generally frusto-conical shaped cover plate composed of electrically conductive material adapted to be secured to the outer terminal structure of the insulator, and at least one toroidal electric field grading ring means composed of conductive material secured to the cover plate near the outer annular edge thereof, an annular drip lip extending around the entire periphery of the ring means, the drip lip including an annular strip of metal secured to the toroidal ring means in substantially an annular path thereon farthest from the axial center of the insulator, and a wire secured to the bottom edge of the annular strip and extending around the ring means.

8. For use with a high voltage insulator, the combination of a generally frusto-conical shaped cover plate composed of electrically conductive material adapted to be secured to the outer terminal structure of the insulator, and at least one toroidal electric field grading ring means composed of conductive material secured to the cover plate near the outer annular edge thereof, an annular drip lip extending around the entire periphery of the ring means, the drip lip including an annular run-off strip of metal secured to the toroidal ring means in substantially an annular path thereon farthest from the axial center of the insulator, and a wire secured to the annular strip and extending therearound, said wire extending substantially outwardly from the bottom edge of the run-off strip and assisting in preventing water from running around to the underside of the toroidal ring means.

References Cited UNITED STATES PATENTS 1,259,443 3/1918 Randall 174-140 X 1,774,969 9/1930 Grant 174140.2 X 1,848,622 3/1932 Gouverneur 174139 2,298,900 10/ 1942 Peters 174-140 X FOREIGN PATENTS 529,948 7/ 1931 Germany.

912,117 5/1954 Germany.

581,398 10/ 1946 Great Britain.

271,376 2/1930 Italy.

177,045 7/ 1935 Switzerland.

LARAMIE E. ASKIN, Primary Examiner US. Cl. X.R. 17421 1 

